(1) Field of the Invention
The present invention generally relates to a supervisory system for network equipments, and more particularly to a supervisory system for gathering status information via lines from a plurality of network equipments communicated with each other in a network so as to survey the network equipments, the status information indicating status of each network equipment.
Recently, a supervisory system for hierarchically surveying a plurality of network equipments dispersed in a network has been proposed. Due to this type of the supervisory system, maintenance works for the network can be effectively performed and the reliability of communication between network equipments in the network can be improved.
(2) Description of the Related Art
FIG.1 shows a supervisory system for hierarchically surveying a plurality of network equipments. Referring to FIG. 1, a plurality of network equipments 10 are connected with each other by a line 15 so that the communications between the network equipments 10 are performed via the line 15. Each of subordinate supervisory devices (SSV) 20(1) and 20(2) surveys connected to a plurality of network equipments 10, and a middle supervisory device 30 supervises the subordinate supervisory devices (MSV) 20(1) and 20(2). Furthermore, the middle supervisory device 30 is supervised by an outranking system (OSS). In this system, each of the subordinate supervisory devices (SSV) 20(1) and 20(2) are centrally gathering performance data indicating changing of the status (e.g. a bit error rate) of the network equipments. The performance data is further transmitted from each of the subordinate supervisory devices (SSV) 20(1) and 20(2) to the middle supervisory device (MSV) 30. Then, the performance data is finally supplied from the middle supervisory device (MSV) 30 to the outranking system (OSS).
The above supervisory system can be extended to a hierarchical supervisory system as shown in FIG. 2. Referring to FIG. 2, the hierarchical supervisory system has four hierarchies. The first hierarchy is provided with primary supervisory devices (P-SV) connected to network equipments (NE). The primary supervisory devices (P-SV) are set up in remote terminals. The second hierarchy is provided with regional supervisory devices (R-SV) connected to the primary supervisory devices (P-SV). The regional supervisory devices (R-SV) are set up in regions each of which regions includes one or a plurality of the remote terminals. The third hierarchy is provided with extensive supervisory devices (X-SV) connected to the regional supervisory devices (R-SV). The extensive supervisory devices (X-SV) are set up in zones each of which zones is formed of one or a plurality of regions. The fourth hierarchy is provided with a center supervisory device (C-SV) connected to the extensive supervisory devices (X-SV). The center supervisory device (C-SV) gathers the performance data from the network equipments (NE) via the primary supervisory devices (P-SV), the regional supervisory devices (R-SV) and the extensive supervisory devices (X-SV). The primary supervisory devices (P-SV) and the regional supervisory devices (R-SV) respectively correspond, for example, to the subordinate supervisory devices (SSV) and the middle supervisory devices (MSV) shown in FIG. 1. A system formed of the extensive supervisory devices (X-SV) and the center supervisory device (C-SV) corresponds, for example, to the outranking system (OSS). Each unit formed of the extensive supervisory device (X-SV) and the regional supervisory devices (R-SV) under the extensive supervisory device (X-SV) may correspond to the middle supervisory device (MSV) shown in FIG. 1. In this case, the center supervisory device C-SV corresponds to the outranking system (OSS).
In the above system for hierarchically surveying a plurality of network equipments, as shown in FIG. 1, if a supervisory device (the SSV or the MSV) in any hierarchy is troubled, the performance data of the network equipments under the troubled supervisory device cannot be transmitted to the outranking system (OSS). It is thus desired that the outranking system (OSS) estimates trouble points in the network and estimates causes of the troubles based on the performance data gathered from the network equipments. In this case, a matter is a problem in which when a supervisory device in any hierarchy is troubled, the performance data from any part of the network equipments under the problem supervisory device cannot be gathered by the outranking system (OSS).